GA4+7 Soak Before Cold Stratification Enhances Juglans nigra Seedling Production

Eastern black walnut (Juglans nigra L.) seeds typically require a long period of stratification and often have low germination. A study was conducted to evaluate the effect of three formulations of gibberellic acid at 250 mg.L-1 or tap water as a soaking treatment for 'Thomas' black walnut seeds for 24 h before stratification for 30, 45, 60, 75, or 90 d. Gibberellic acid treatments included 1) GA(3) (ProGibb (R)); 2) GA(4+7) (Provide (R)); and 3) 6-benzyladenine (BA) + GA(4+7) (Promalin (R)). Percent walnut shoot emergence 60 days after planting, days to 20% and 80% shoot emergence (E20 and E80), and early seedling growth from black walnut seeds were evaluated. Percent shoot emergence was always higher for seeds soaked in GA(4+7) or BA + GA(4+7) when compared with other treatments. Shoot emergence for some seeds soaked in GA(4+7) and BA + GA(4+7) occurred with 30 d stratification and percent emergence increased with longer stratification periods. Seeds soaked in GA(3) had higher percent shoot emergence than those soaked in tap water only. Also, seeds soaked in GA(3) had fewer days to 20% shoot emergence when stratified for 45 or 60 d than those soaked in tap water and stratified for the same period of time. Addition of BA at 250 mg.L-1 apparently did not enhance percent shoot emergence, E20, E80, or seedling height or weight. With timely harvest, hulling, seed selection, and soaking walnuts with 250 mg.L-1 GA(4+7) followed by 90 d stratification, 82% shoot emergence (i.e., germination) was attained.